1. Field of the Invention
The present invention relates to a street-sweeping machine.
2. Prior Art Involving Rear Mounted Pick-up Brooms on Truck-Type Sweeper
In previous designs of truck-type broom sweepers, with the dirt hopper near the middle of the vehicle, the pick-up broom at the extreme rear, and a conveying mechanism in between the broom and hopper, it has been the practice to suspend the pick-up broom from the rear of the vehicle with just enough vertical movement of the broom so that it would reach the ground for sweeping and lift off of the ground for vehicle transport, and just high enough to clear the ground when the vehicle traversed over rough roads, at dump sites, or when starting or exiting from an incline such as a driveway or ramp.
This small amount of vertical broom movement required the simplest lift mechanism but resulted in several disadvantages which are:
1. Extended the overall length of the vehicle when transporting that made vehicle maneuverability in traffic and when parking more difficult. PA1 2. Extended the overhung length behind the rear axle of the vehicle which made the broom vulnerable to hitting light poles and signs during a short radius turn. This also resulted in additional cantilever loading on the rear axle which was already heavily cantilever loaded due to other mechanism such as auxiliary engine and water tank located behind the rear axle. PA1 3. Relied on hydraulic pilot operated check valves to hold the broom in the "up" position while the sweeper was being stored overnight, over weekends, or extended periods when the weather was not conducive to sweeping. Hydraulic pilot operated check valves normally allow some oil to leak through thus allowing the broom to drop to the ground. If the broom is permitted to stay on the ground for several days, the bent broom fibers often take a permanent set which produces a flat spot on the broom, throwing it out of balance thereby causing early and expensive broom replacement. PA1 4. Some prior broom suspensions relied only on the weight of the broom and broom arms to hold the broom center at the correct distance from the road for sweeping. The broom was limited in distance from the center of the broom to the surface of the road by a chain or cable to give a correct sweeping pattern, but only relied on the broom and suspension weight to keep the broom on the ground. When the rear wheels of the sweeper would go over a ridge or rough spot or hole in or on the road and where the broom was cantilevered about the sweeper rear axle, the main broom would have a tendency to bounce and lift off the road resulting in strips of unswept dirt being left on the road. In the sweeper art, this unsatisfactory operation of the main broom is commonly referred to as "broom skipping" or "broom bouncing". PA1 1. The broom suspension shortens the overall length of the sweeper during transport. PA1 2. The broom suspension reduces the overhung weight behind the rear axle thus making the sweeper more stable and the ride more comfortable when the sweeper is in transport to and from sweeping sites and/or dump sites. PA1 3. The broom suspension has a reverse ramp on a swivel cam that mechanically locks the main broom in the "up" position with the center of gravity of the broom only slightly to the rear of the suspension pivot point. Therefore, no hydraulic locking valves are required to hold the broom up. PA1 4. The broom suspension performs the 130.degree. approximate translation of the main broom with a simple linkage and lever system activated by a single hydraulic cylinder. PA1 5. The broom suspension incorporates an adjustable broom snubber to provide controlled friction in the broom suspension arms so that the tendency of the broom to bounce up is reduced while still allowing the broom to work at the normal lowest position limited by a stop chain. The stop chain is fastened to an extension spring designed to allow the broom to automatically follow the contour of a depression or dip in the surface being swept. The width of broom contact commonly known as "broom pattern", in the depression is reduced from the width on a flat even street, yet this small amount of allowable movement prevents dirt from being deposited in transverse depressions in the street which depressions are encountered in normal sweeping. The concept of using an extension spring or compression spring in the broom suspension to allow the broom to sweep shallow depressions has been used in the past.